package com.yang.sqlSession;

import com.test.pojo.User;
import com.yang.pojo.Configuration;
import com.yang.pojo.MappedStatement;

import java.lang.reflect.*;
import java.util.List;

public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(String statementid, Object... params) throws Exception {
        //将要去完成对simleExecutor里的query方法的调用
        SimpleExecutor executor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        List<E> list = executor.query(configuration, mappedStatement, params);

        return list;
    }

    @Override
    public <T> T selectOne(String statementid, Object... params) throws Exception {
        List<Object> objects = selectList(statementid, params);
        if(objects.size()>0){
            return (T) objects.get(0);
        }else{
            throw new RuntimeException("查询结果为空");
        }
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        // 使用JDK动态代理来为Dao接口生成代理对象，并返回
        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass},
                new InvocationHandler() {
                    @Override
                    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                        //底层还是去执行JDBC代码 //根据不同情况，来调用 selectList或者 selectOne
                        //准备参数 1：statementid : sql 语句的唯一标识： namespace.id = 接口全限定名.方法
                        //方法名 selectList
                        String methodName = method.getName();
                        String className = method.getDeclaringClass().getName();

                        String statementId = className+"."+methodName;

                        //准备参数2：params
                        //获取被调用方法的返回值类型
                        Type genericReturnType = method.getGenericReturnType();
                        //判断是否进行了泛型类型参数化
                        if(genericReturnType instanceof ParameterizedType){
                            List<Object> objects = selectList(statementId, args);
                            return objects;
                        }
                        return selectOne(statementId, args);
                        //TODO 后续再添加其余语句
                    }
                });

        return (T) proxyInstance;

    }


}
